Engineers are constantly seeking ways to reduce undesirable emissions from engines. Over the years, engineers have come to recognize that cleaner burns tend to occur when there is a better mixing of fuel and air prior to combustion. One relatively recent strategy for improving fuel/air mixing is commonly referred to as homogenous charge compression ignition (HCCI). In an HCCI strategy, fuel is injected into the engine cylinder early in the compression stroke. The liquid fuel vaporizes in the engine cylinder and mixes with the air to produce a relatively lean homogenous mixture. As the compression stroke continues, the homogenous charge ignites when pressure and temperature in the cylinder reach the auto-ignition point. Although an HCCI strategy can produce a relatively clean burn with dramatic reductions in undesirable emissions, it remains problematic both in the ability to control ignition timing and operate a given engine in a HCCI mode at high load conditions.
One method attempting to control ignition timing in a homogenous charge compression ignition engine is taught in U.S. Pat. No. 5,875,743 to Dickey. Dickey appears to assert that ignition timing can be controlled by injecting a controlled amount of water into the air brought into the cylinder through the intake valve. Although the usage of water may be a viable strategy in controlling ignition timing in an HCCI engine, there remains the problem of HCCIs' general incompatibility with higher engine loads.
At higher engine loads, when the amount of fuel injected is substantially higher than that at lower loads, the very efficient HCCI burn also becomes a liability. Apparently, when a HCCI charge burns, there is little or no flame front, and the entire charge combusts almost simultaneously over a relatively brief duration. With the burn duration being relatively short, the pressure spike produced by the burn can be destructively too high at higher engine loads. Thus, in order to make HCCI viable, ignition timing needs better control, and the combustion duration must be sufficiently long as to not overstress the engine, especially at higher loads.
The present invention is directed to one or more of the problems set forth above.